Permeability tuning system



Nov. 27, 1945; w. R. KOCH 2,389,986

PERMEABILITY TUNING SYSTEM 21 g ff AWL.

Filed June 11, 1943 INVENTOR ATTORNEY Patented Nov. 27, 1945 Winfield R. Koch; fladdonfield, N. J assignor to Radio Corporation of America, aicorporation of Delaware PDlicationJune 11, 1943;1sei-iai No. 490,411

'8 Claims.

My present-invention relates toa variable permeability tuning system for superheterody ereceivers, and more particularly to vthe core and coil structure utilized in the signal frequency and oscillator circuits .of such receivers for effecting tracking between said circuits.

In receivers of the .superheterodyneitype it is essential for satisfactory operation that the resonant frequency of the signal circuit'difier from that of the oscillator circuit by substantially a :constant :amount, this difierence frequency being commonly known asthe intermediate frequency. It is the usual-practice to tune the oscillator circuit through a frequency range higherthan th range through which the signal circuit is tuned. As a :result in :order to insure a constant frequency difierence :the frequency range of the oscillator :circuit must 'beunarrower in percentage, and if the variable tuning elements of the two circuits are to be uni-controlled, is the usual ractice, suitable means must beprovided whereby .the frequ ncy variation o f the 0 scillator circuit must be (slowed up-.in orderto keep in step with the frequencyyariation of the signalcircuit.

It is therefore one of zthe 'objects of myqim e tion to provide, in a isuperheterodyne radiome- .ceiver, an improvedvariable permeability tuning system ;for causing the oscillatorzahd signal input circuits to track accuratelyone with the other throughout a predetermined frequency range.

:There are several known :methods (and forefiecting'tracking'in the tuning-oftwoorimore circuits by variable permeability tuning :means, some of ,which are impracticable becauselof cost 1 or manufacturing dificulties. One known methof ofsecuring tracking :in a permeability-tuned superheterodyne receiver for the I broadcast :band

' uses a variable-pitch winding :on theuoscillator coil. Other methodshave includedshapedcores, tapped-coils, :or a :two-section .coil, so-:that :the core enters "one section while "it is leaving :the other section.

v In :the .systemaccordingE-to the present invention,-asingle :constant-pitchcoil is usediin'rthe i oscillator :circuit abut it 518 so dimensionedwand positioned that :as the oscillator core iis'iwitkldrawn from its coil (in tuning the receiver to -a higher frequency) the core .thatis withdrawn from the coil included in ,radio frequency circuit enters the oscillator coilsin order to b.. tainttracking;

.Jt is ;a further objector thednvention-to er.- m th '10801118't01 tuning inductance coaxially and in an axially .spaced relation on a co m n @011 form, r .on separ te 001. f rm of different diameters, the cores for the respective coils ineach case being arranged to .m ve in unison and ina manner such that at the h h frequency endsofvthe range. as the coil for the signal frequency circuit is withdrawn from its associatedcoilitsenters the oscillator coil winding to vobtain thereby a predetermined relation in inductance variation of said coils withthecore adjustment.

Still .-another obiect is to provide an auxiliary oscillator winding so arrangedon the coil form that at .the high frequency end of the range it is influenced by the core of the signal frequency circuit in a desired manner to eiiect trackin betweenmthesignal frequency andoscillator frequency circuits.

Still a further object is to provide ..a simple and inexpensive vconstruction for the variable tuning inductors of two circuits which are to be tuned by thesame-control and which are to be ma ntained at a constant frequency difference.

The invention will be further understood however from the following description, when consideredinkconnection with the accompany drawing and its scope is pointed out in the appended claims.

r cpimmrtes .a typical c r .a nin jor .avsuperheterodyne receiver which. will s e to p a n t e a p i at n y o h p ent inve t onnand 12, 3 @-I1ti4 8 1'1 O,W various core coil arrangements in accordance @with the inventiom Referring firs t:--to Fig- 1 which illustrates a t ica r-c nv ie circ i o a s p r d receiver,-the tunablesignalinputcircuit .is shown at ,1 and ;the :ttmable ;oscillator circuit ;at 2. In t e s sn l'i pu rcui the :t a iable tunin inductance L, is provided with ,a movable tuning core indicated at- Ce, while ;in vthe =oscillator or second circuit,; thegtuninginductance Lo is provyided with a movable tuning core .Co connected wi h the firs c re a i di a b t dot ed 511 in er unitary t ning control movement- The circuit I includes-a shunt-tuning capacitor 4 :tor an a s u t t m r l apafii e ,1318 fih erbe ngadjusted to establish the low frequency; end of the tuning range when the core Cl is moved fully within winding Is.

circuit l isconnected to ground as .indicatedatai and isconnected at its high potential tunipglinductanceuof thesignal frequency circuit 4 s o csu table- -siznal source, such as. an

the low frequency end of the tuning range of the The oscillator circuit 2 in the present example is 'of the Colpitts type, having a cathode con-i111 nection ll between the capacitors 9 and 10, and being grounded as indicated at 12, at the low po tential side thereof.

The input circuit is contestants-ma f,

tential side to a signal input grid l3 of a combined detector-oscillator tube I4. The cathode I5 is connected to ground lfithrough'a suitable R. 1". choke coil II, the cathode terminal I8 o which is connected with the cathode tap II of the oscillator'circuit."

The circuit 2 is connected with asecond-"s'i nal grid l9 inthe tube M'for electronically'mixing thesignals from the circuit 1 with oscillations to produce a predetermined intermediate frequency in the output anode circuit'20 of the'detector oscillator tube. Feedback for the production of oscillations is provided "in connection with the screen grid 2|;w-hich functions as an anode coupled to' ground through a by-pass capacitor 22 in connection with a filter resistor 23 in the screen grid supply'circuit indicated at 24. Theoscillator'grid is provided with the usual grid coupling capacitor 25 and 'gridjleak 26'to In connection with the'circuit l and 'thesignal input grid" l3, a coupling capacitor 21 and grid resistor 28 are provided, the latter being connected to a bias supply lead 29 ,with a suitable by-pas's to ground through a 'by-pass capacitor 30; Signals are derived from the output circuit of detector-oscillator through a suitably tuned intermediate frequency coupling transformer 31. 'Referring now toFig. 2 alongwith Fig.'"1,the same referencech'aracters' are. used todesignate like parts as in the preceding figure, the signal input. circuit inductance being indicated" at Ls and the oscillator tuning inductancebeing indicated' at 'Lo and theirqrespective tuning' cores being shown at Csiand Co; Theinductance wind' ings are each'of constant or uniform pitch and are coaxially arranged and axially spaced on a "common insulating cylindrical coil form32 within which the cores are adaptedto be reciprocated. Theinner opposing ends of the cores are con I0 alone, the core Co may be adjusted relatively to the core Cs as by varying the length of the 7 connecting rod .33, so that its position corresponding to the fully entered position 38 of the core Cs will be as shown by the dotted line 39. Since the oscillator core L0 is of uniform pitch, adjustment of its core Co in tuning the oscillator circuit toward the highfrequencylend of the range will-result in a decided departure from the desired tracking frequency. In order to compensate for this departure it is arranged that as the core C5 is withdrawn from its associated coil Ie'it entersinto the field of the oscillator coil Lo, thereby; increasing the inductance of thelatter coil and slowing :up the frequency variation of the oscillator circuit to a sufficient extent to cause it to track properly with the signal circuit. 'In Fig. 3 an alternative arrangement for obtaining proper tracking is shown; separate coilforms for the signal and oscillator coils being used." As illustrated the oscillator coil Lo-is mounted onthe larger diameter coil formJ-l;

sincethe increase inthe coil diameter has the effect of slowing up the'irequency variation of fication is like that shown in Fig. 2 andwill-operate in substantially the same manner. I y

In Fig. 4,-'as in Fig. '2, acommon coil form 42 is used, there being-provided however-an auxiliary oscillatorcoil winding-L02 spaced-from and suitably connected, in series or in parallel, to the main oscillator coil L01. In operation, asthe' core Cs is moved to tune the signal circuit toward :the high end of the frequency range it is gradually withdrawn from the signal coil Ls and permitted to enter the field of the auxiliaryloscillator coil L02, thereby increasing the inductance of the lat -ter and afiecting the oscillator circuit in a man ner similar to that described in connection with nected by means of arigid'member; such asthe 7 rod 33, and the-extreme outer ends of the cores are connected to suitable flexible means-such as a-cable 34 which is entrained about idler pulleys ferred" embodiments of my invention, it-ivill jbe 35xand-an operating control shaft36, the latter range. In orderthat the oscillator circuit'rnay track with the signal circ'uitat-the'low end of the range more accurately than can be obtained by adjustment of the trimmer condensers i and the previous modifications. I

I In the modificationsdisclosed in Figs. 2 and 4 the coils Ls and L0 (or L01) do not-necessarily have tov be-of-the same length, diameter orwire size, no do the length, diameter; or permeability of thecores Csiand Co have to be the same, althoughirom the standpoint cit-"lower production cost it would be desirable to have coil's and cores of similar dimensions; In Fig; 4 the pitch, diameter or wire sizeof the two sections Lorand Loz of "the. oscillator? winding :do not have to -be the same. The coils'inlthis case do not have to be near one another." .Eorjeachiapplication, however, itis necessaryto determine by trial or-cal- 'cu1ation, the dimensions, permeabilities, etc.,'1of the cores and coils whichw'ill :comeclosest tothe true desired tracking.

WhileI' have shown andidescribed certain understood that 5 various e modifications land changes will occurto those skilled in the art with- -out departing from .the spirit and fscopewoi this invention. 7 I therefore gkcontemplate' by: the ap .pended" claims lto cover; any such. modifications as fall within thetrue spirit and scope. of :my 5111- vention; q 1 1' .1 T: i .if: .Wha'tI claim is: V 1

1. In :a ermeability l tuning" seam i orradio apparatus having a pair of circuits to be tuned, each of said circuits comprising-1a tuning 'coiland a movable magnetic tunin'g cbre", said :tunin'g coils being coaxially 1 arranged iand 'tIiir respective -cores so constructed 'an'd" arranged.

with respect to each other and with respect to the coils that a one of the cores is withdrawn from its associated coil it is caused to enter into the other coil to thereby effect a predetermined tracking relation between said pair of circuits.

2. In a permeability tuning system for a superheterodyne receiver havin a signal frequency circuit and an oscillator circuit, said circuits each comprising a tuning coil and a movable magnetic tuning core, said coils each being of uniform pitch and coaxially aranged, and said cores being so constructed and arranged with respect to each other and with respect to the coils that as the signal frequency core is withdrawn from its coil it is caused to enter into the oscillator coil to thereby effect a predetermined tracking relation between said signal frequency and oscillator circuits.

3. In a permeability tuning system for a superheterodyne receiver having a signal frequency circuit and an oscillator circuit, means for effecting tracking between the signal frequency and oscillator circuits over a predetermined frequency range comprising a tuning coil and a movable tunin core for each of said circuits, means for moving said cores in unison to tune the system through said frequency range, said coils each being of uniform pitch and coaxially arranged, and said cores being so constructed and arranged with respect to each other and with respect to their coils that upon simultaneous adjustment of the signal frequency and oscillator cores the inductance variation of the oscillator coil at one end of the frequency range is brought about by the joint action of both cores upon the oscillator coil.

4. In a permeability tuning system for a superheterodyne receiver having a signal frequency circuit and an oscillator circuit, means for effecting tracking between the signal frequency and oscillator circuits over a predetermined frequency range comprising a tuning coil and a movable tuning core for each of said circuits, means for movin said cores in unison to tune the system through said frequency range, said coils being coaxially arranged and at least the winding of the oscillator coil being of uniform pitch,

the cores being so constructed and arranged with respect to each other and with respect to their coils that as the signal frequency core is withdrawn from'its coil to tune the system to a higher frequency it is caused to enter into the oscillator coil.

5. In a permeability tuning system as defined in claim 4, wherein the coils are mounted on a common insulating tubular form.

6. In a permeability tuning system as defined in claim 4, wherein the coils are mounted on separate insulating tubular forms of different diameters.

'7. In a permeability tuning system for a superheterodyne receiver having a signal frequency circuit and having an oscillator circuit, means for effecting trackin between the signal frequency and oscillator circuits over a predetermined frequency range comprising a tuning coil and a movable tuning core for each of said circuits, means for moving said cores in unison to tune the system through said frequency range, an auxiliary coil associated with the oscillator tuning coil, said coils being coaxially arranged and at least the winding of the main oscillator coil being of uniform pitch, said cores being so constructed and arranged with respect to each other and with respect to their coils that as the signal frequency core is withdrawn from its coil to tune the system to a higher frequency it is caused to enter into the auxiliary oscillator coil.

8. In operating a tuning system which includes two circuits each havin a coil and a relatively movable ferro-magnetic core to tune said circuits over upper and lower frequency ranges respectively, the method of regulating the inductance variations produced by the relative movement of said coils and said cores to maintain said circuits at a substantially constant frequency difference, which consists in the step of causing the core associated with the coil of the circuit operating over the lower frequency range to enter into the coil of the circuit operating over the upper frequency range and thereby partly affect the inductance variations of both coils at one end of said frequency ranges.

WINFIELD R. KOCH. 

